The present invention relates to a source driver, an electro-optical device, and an electronic instrument.
In an active matrix type liquid crystal display (LCD) panel (electro-optical device in a broad sense) or the like, source lines may be driven by a multiplex drive. When forming a demultiplexer on an LCD panel, a source driver which drives source lines multiplexes grayscale voltages corresponding to grayscale data of dots forming one pixel by time division, and supplies the multiplexed grayscale voltage to the LCD panel. The demultiplexer separates the multiplexed grayscale voltage into the grayscale voltages corresponding to the source lines. In this case, the number of source outputs of the source drivers can be reduced.
When a demultiplexer is not formed on an LCD panel, a source driver is configured to include a demultiplexer. In this case, the circuit of the source driver can be used in common for the time-division multiplexed dots, whereby the circuit scale can be reduced.
Precharge technology is known which increases the liquid crystal drive speed of such an LCD panel. According to this precharge technology, a source line is precharged to a specific potential before driving the source line based on grayscale data, thereby reducing the amount of charging/discharging of the source line along with supplying a drive voltage based on the grayscale data.
This precharge technology is disclosed in JP-A-10-11032, for example. In JP-A-10-11032, different direct-current potentials are provided in advance, and a switch is provided between each direct-current potential and a source line. A connection between the direct-current potential and the source line is controlled by controlling the switch corresponding to the polarity of liquid crystal inversion drive. According to this precharge technology, the amount of charging/discharging of the source line along with driving can be reduced, even if the precharge cycle is reduced, whereby the liquid crystal drive time can be reduced while suppressing an increase in power consumption.
The precharge technology disclosed in JP-A-10-11032 changes the potential of the source line before the drive period in order to reduce the drive period. Therefore, the precharge voltage need not have a high accuracy.
In recent years, the resolution and the number of grayscales of an LCD panel have increased remarkably. Therefore, when the effective values of the voltages written into pixel electrodes differ, the difference in grayscale display between pixels can be clearly identified. The effective value corresponds to the integral value of the voltage applied to the pixel electrode in one horizontal scan period, for example. Therefore, even if pixels are connected with source lines to which an identical grayscale voltage is supplied, the difference in grayscale display can be identified when the precharge voltages differ, whereby the image quality deteriorates. In particular, since the grayscale characteristics cannot be changed in units of multiplexed pixels when using a multiplex drive in which the source lines are driven using the grayscale data of two or more pixels, the image quality deteriorates to a large extent due to the difference in precharge voltage.
A source driver which drives the source lines of such an LCD panel is divided into two source driver blocks from the viewpoint of layout efficiency, for example. The source lines in the left display area of the LCD panel and the source lines in the right display area of the LCD panel are driven by the respective source driver blocks. Therefore, when the precharge voltage differs between the two source driver blocks, the boundary between the left display area and the right display area of the LCD panel is identified, even when displaying an identical grayscale value.
Since the above problem is caused by the effective value of the voltage applied to the pixel, the above problem is applied not only to a source driver which multiplex-drives the LCD panel, but also to a source driver which does not multiplex-drive the LCD panel. Therefore, it is desirable that the source driver which precharges the source lines before driving the source lines be able to set the precharge voltage with high accuracy.